linux-kernel - Re: APIC priorities, can they be changed?

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Date:	Thu, 15 Feb 2007 14:57:06 -0500
From:	Mike Panetta <m.panetta@...ener.com>
To:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: APIC priorities, can they be changed?

linux-os (Dick Johnson) wrote:
>
> On Thu, 15 Feb 2007, Mike Panetta wrote:
>
> > I am not on the list (corperate email sucks) so please CC any replies to
> > me.  Thanks.
[snip]
> > I have seen the preempt patches, but they touch a lot of files, and we
> > have gone through testing with the 2.6.16.19 kernel and do not wish to
> > change, and we cannot find a version of the patch for this kernel. Is
> > there something smaller/simpler I can do?  My understanding is the
> > priority in the APIC is set in software via the interrupt vector number
> > (higher numbers have lower priority) is this true?  If so, how hard
> > would it be for me to just change the vector numbers around?
> >
[snip]
> > Thanks,
> > Mike
>
> Can't you muck with the BIOS settings? That's where the primary
> hardware gets 'connected'.
>

I did try that.  The BIOS only allows me to either allocate an IRQ to be 
a PCI interrupt, or reserve it (for what I have no idea).  The IRQ's 
listed in the BIOS are also different from the ones Linux sees.  I think 
the BIOS is seeing the XT-PIC IRQ numbers and Linux is seeing the APIC 
numbers.  For example the little bios blurb that prints before the 
system boots says the USB controller I am interested in is 
assigned/using IRQ 10, Linux sees it using IRQ 18.

I have found that I can keep Linux from using the APIC by disabling it 
with a kernel command line switch, but that does not help, it just makes 
Linux use the XT-PIC instead of the IO-APIC to do IRQ routing.

So I guess I'm back to my original question of  'Would changing the 
vector numbers do what I want?' and if the answer is 'yes', how would I 
do it?

Thanks,
Mike

>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.16.24 on an i686 machine (5592.61 BogoMips).
> New book: http://www.AbominableFirebug.com/
> _
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